


Differential

by flannelcastiel



Category: Supernatural
Genre: Alternate Universe - High School, Alternate Universe - Human, Anal Fingering, Anal Sex, Bottom Dean, First Time, Human Castiel, Loss of Virginity, M/M, Shame, Size Difference, Size Kink
Language: English
Status: Completed
Published: 2013-07-29
Updated: 2013-07-29
Packaged: 2017-12-21 19:33:05
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,301
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/904045
Author URL: https://archiveofourown.org/users/flannelcastiel/pseuds/flannelcastiel
Summary: <blockquote class="userstuff">
              <p>In which Dean and Castiel are about to be each other's firsts, but Cas has a <i>big</i> surprise.</p>
            </blockquote>





	Differential

**Author's Note:**

  * For [cupidwithapistol](https://archiveofourown.org/users/cupidwithapistol/gifts).



> In short, the prompt for this one (from Tumblr) was literally "Cas has a huge wee wee and Dean's embarrassed so he doesn't wanna take off his pants." One thing led to another...

Dean's hands are actually  _trembling_ when he brings them to Cas's face, cupping the underside of both sides of his jaw as they share a deep, seamless kiss. He's excited—in more ways than one—and he's terrified too. As much as he puts on a game face and acts like he's a sex guru, he's a virgin. A  _virgin_.

Not for long though. Dinner and a movie, that's what has filled the hours prior to the soft yet desperate tumble of their heated, horny bodies into Cas's bed. His parents are out of town, and even permitted Dean to stay over. It's no secret that the two of them have been dating for months now, but they are both eighteen and have been bound at the hip since elementary school. Dean hasn't said it aloud, but he's pretty sure he's signed the dotted line—Cas is the person who he plans to spend the rest of his life with.

So it makes no sense, why Dean is so unsure. He blames it on nerves, he blames it on drinking five Cokes at dinner (out of being nervous, obviously). Cas, on the other hand, is solid and steady and thumbing circles at the base of Dean's neck. It's comforting, and Dean can feel his concern as their lips break apart for a minute.

"Dean if you aren't ready..." he whispers, and Dean's skin blushes and he silences the heat by shoving his lips back to Cas's. He moans into it, expressing his enthusiasm, which causes Cas to smile.

Dean starts to pull off Cas's clothes, starting with his shirt. He's seen his boyfriend shirtless, but he's never got to touch him like this. He presses Cas back against the mattress, straddling his hips as he attends to the soft, tan plane with his fingers. He finds himself getting lost in the trail of hair that begins between his nipples, travels down his stomach, and recedes past his pant line. He wants to see the trove where the trail leads, so he wastes no time in undoing Cas's pants while leaning down to kiss his stomach.

Dean is  _still_ shaking, breathing like he's just ran a marathon, because it's about to happen. His lips are sucking little bruises into Cas's stomach, and he's already pulling Cas's pants down his thighs. The only thing between his hand and his boyfriend's cock is a freaking pair of boxer shorts.  He inhales and closes his eyes, willing himself to just dive in. He loves Cas. He can do this.

His hand breaches past the waistband and he follows the hair to Cas's groin, feeling the erect length brush his palm, wet and hot and  _thick._ Dean shudders a hot breath, suddenly anxious for more. He tugs the boxers off in a rush, licking his lips.

His mouth falls open. No—his freaking jaw comes unhinged when he sees Cas...sees his cock.

It's—it's fucking  _huge._ His eyes open wide as saucers, color draining from his face. Cas moves just a little, leaning up to see the reason for pause, and the tip of it pokes Dean in the cheek. It's like he's slapped in the face, because Dean's scrambling away from Cas, eyes glued between his legs.

Holy  _mother fucking shit_ —his boyfriend, Mister I-have-a-four-point-three-grade-point-average Castiel Novak—has a monster dick! It's not just thick, like Dean felt when he gave it a squeeze, but it's long. Even erect and curved, it's still got at least three inches on Dean's. And he's not even  _small—_ but he never thought—he's dating a freaking  _sex god._

"Dean?" Cas says, and Dean can barely hear him when Cas murmurs his name again. He's got cotton or something shoved in his ears, eyes glued to the throbbing dick that he'd just distanced himself from. He blinks, forcing himself to look away, but he can't look Cas in the eye.

This was supposed to be perfect. Dean did the romance thing, the gentlemen thing, the flirtation and foreplay—not to say he didn't normally enjoy those things—because it was leading up to the most important stepping stone in their relationship. Kissing and touching was nice, but it didn't really shatter the friendship mold they'd been living in for years. This was supposed to be that earth shattering moment—and Dean's struck with the realization that the dick he'd planned to fuck his boyfriend with is just a little stub in comparison. Nothing kills a boner like that.

Dean runs a hand through his hair, closing his eyes as he attempts to lock down every demoralizing thought his mind comes up with. It shouldn't start and end with how big his dick is, but he just can't—he's—

" _Look at me,_ " Cas intones, grabbing Dean's wrist and earning his gaze with the rough gesture. "What happened? Please talk to me?" His voice is a little higher, more along the lines of desperate than angry. "Dean."

He does look into Cas's eyes, but it makes his cheeks run hot again. "We should do this—later," Dean croaks.

Cas's face softens, and suddenly he's smoothing a hand down his shoulder. "Dean..." It's comfort, it's warm, and it's basically the reason why Cas has always been his confidant. The very touch of him cleanses the toxicity of his own thoughts, fears. Mostly, anyways—Dean still feels the thrumming of his heart and the whispering of insufficiency in his thoughts.

"Please?" Dean asks. "I—I am freaking out here. I can't—"

"I am not arguing. I am definitely not ready to do this if you're not," Castiel cuts in. "Why would I continue to ask you, when you're so obviously torn up about something? But I want you to talk to me."

"I can't..." Cas raises an eyebrow "Uh...I feel sick, and I don't want to get my germs all—all over your..." Jesus, fuck, he can't even think of Cas's cock without his face going red and his legs pulling tight underneath him. He wants to run, preferably to his house and to his room where he can hide under his blankets forever. And maybe with a stolen beer from his Dad's minifridge.

"Okay..." Cas trails off, reaching for his boxers. Dean pointedly tries not to watch as Cas tucks his huge dick back in the plaid of his shorts. But he sees it. And he swears his own is withering away like a dried out vegetable. Cas crosses the bed again and tugs on Dean's wrists. He resists, but gives into the motion and lays down innocently beside Cas.

He breathes, because this is normal. Before they started dating, Dean often laid next to him. Sometimes, he dreamed that one day they  _could_ fuck on this very mattress, but he never dreamt they'd end up like this. This is definitely not his fantasy. Cas weaves his fingers into Dean's, and then pulls their intertwined hands to his mouth. He freaking starts kissing Dean's knuckles, like he's something to adore. If he only  _knew_ that—that he was average-sized with no means to compensate except his good looks. He doesn't know what kind of stops to pull, to make up for being so much shorter, so he can only assume that Cas won't want him. It's a ridiculous thought, because they are in love, they are best friends—but it sticks with Dean anyways.

"I love you," Cas whispers, and their eyes are locked together in an infinite gaze that kind of supersedes every negative thought flowing around in Dean's head.

He swallows. "I love you too, Cas," he promises. "I'm sorry."

"Why are you apologizing? Is it because I..." Cas turns pink a little, his lips curving into a frown. "I'm not satisfactory?"

Dean's eyes pierce him, wide and disbelieving. "What? No!"

"Then what is it?" Cas demands. "Why did you take one look at my dick and squeam out?"

"Because!"

"It is—I am not aware of the standard size of the male penis because I never thought..." He closes his eyes tight. "I never thought it would matter if I wasn't good enough."

Dean's heart skips a beat and the only thing he can think to do is shove his lips against Cas's. They are tight and unresponsive at first, his hand going limp in Dean's, but Dean tries to kiss that thought out of him. Their lips part, and Dean just trails little desperate kisses across his chin, his cheek, and down to his ear. "You are the best thing," Dean whispers to him, hot and torn and just  _pissed_ that. "You are—you are better than what I ever...ever could have hoped for...better than I deserve..."

"Stop that," Cas says, swatting him away. "Stop talking like I'm some sort of prize—we are equals."

"But we aren't and that's just a fact of life." Dean's voice takes an annoyed curve.

"I want to know what brought this on, if not me," Cas snaps back. "Dean—I don't want to end this—I don't want to lose you—"

"You aren't gonna lose me." Dean sighs, and closes his eyes. He take a minute to just lean back into the pillows, "Cas...do you know how fucking  _huge_ your dick is?"

Cas blinks, staring. "Excuse me?"

"Your. Dick. Is. Huge."

"I..." Cas begins to stammer, turning red. "I wouldn't know—it's the only one I've ever seen?"

Dean feels a rush of warmth, pleasant warmth, because he's just so wonderfully naive. "Dude...you're at least 8 inches long..."

"And that's—that's abnormal?" Cas whispers.

"I think there are dudes who would sell their soul for that—that much dick." Dean shifts uneasily.

"Are you one of them?"

Dean snorts. "I wouldn't have—no, not until I was suddenly faced with one..."

Cas's brows furrow. "I want to see yours."

"No," Dean laughs. "Not tonight."

"I won't do anything," Cas clarifies with the hint of an eye roll. "It's only fair. You got an eye full of mine, I deserve some reciprocation."

"I show me mine, you show me yours," he chuckles. Dean shifts uncomfortably, pressing his thighs together. "It won't be impressive."

"Let me be the judge of that, Dean Winchester," Cas says, and he can hear the warning in his boyfriend's voice. He closes his eyes, trying to blot out his own vision as he slowly reaches for the button of his jeans. It pops open easy enough, and he's lifting himself so he can shimmy out of them. Cas helps by leaning down and pushing the pants past his ankles and to the floor with Cas's own clothes.

It seems like Cas is careful not to touch Dean or help remove his boxers, though, which he's a little grateful for. He's furiously red and sweaty and just embarrassed when he pulls his boxers down, the fabric easing down his ass and thighs slowly. When the cold air hits his dick, he hisses, feeling himself harden a bit out of reflex. _  
_

He glances up to Cas, who's staring between his legs with stars in his eyes. Dean's chest tightens with a little hope when Cas licks his lips, hunger staining his pupils as they blow out, consuming the rings of blue. He fidgets, leaning his head against the headboard with a loud thump that hurts his scalp, but at least he's distracted from his heart beating so hard his rib cage rattles.

"It's so..." Cas starts off, and the litany of internalized insults splay through Dean's thoughts without cause— _small, puny, insignificant—_ "...beautiful."

Dean's lip twitches, and he has to blink. He dares not ask Cas to repeat himself, because he  _heard—_ and Cas is suddenly staring into his eyes like Dean's a unicorn. A freaking majestic unicorn. That's how Cas is looking at him—and if his dick doesn't give a numb throb, he's imagining things.

"But..." Dean starts.

"Don't." Cas slides up the bed, crawling toward Dean. He doesn't let their bodies touch, but he somehow manages to hover above Dean's head so that their lips can smooth together. Dean sighs into it, kisses him back, but neither of them let it become sloppy or desperate. It's steady. It's slow. And it ends sweetly, which then leads to Cas pushing their foreheads flush together. "If I tell you that your cock is beautiful, you are going to believe me."

The words are tinged with  _obey_ , and it caused Dean to shiver slightly. "Okay," he concedes, because he does not see any room for compromise.

"You don't believe me," Castiel murmurs. Dean is silent, which he rightfully interprets as a confirmation. Cas sighs and pulls away, bringing a hand to settle on Dean's shoulder as he balances his weight, continuing to limit skin contact. "After all this time, you don't trust me?"

"How do I know your not just sayin' it...to make me feel better..."

"Dean," Castiel snaps. "Have I  _ever_ said anything for your ego's benefit?"

"No..."

"Then," he whispers lowly, coarse yet soft, and brings his lips to Dean's ear. Cas's teeth graze the shell slightly, his hot breath pouring down and all around Dean's lobe, his neck. "You should know I could never,  _ever_ think poorly of anything at is you. I love everything about you. And I've  _dreamt_ of this night, only to be sharply reminded of your low self-worth." His eyes close. "It hurts, to know that you could ever be ashamed of any part of you—especially the most  _intimate_ part of you."

Just as the words leave his lips, Cas is attaching his mouth to the side of Dean's neck, kissing roughly until Dean's sure that's  _sucking_. Dean shudders, hands raising to cradles his face and curl in the dark mop of his hair as he marks Dean's skin. And just like that, Cas is also sucking away the bitter thoughts and emotions this evening wrought. He whimpers slightly as he feels his neck beginning to bruise, a mark sure to be left for all to see—and  _fuck_ if his core body temperature didn't spike at the mere thought of walking around school Monday baring evidence that he belongs to  _Cas._ And they'd assume they'd done the deed, too, but Dean doesn't know if he can do it. He's a pathetic excuse for a horny teenager.

Cas's lips pop off and he begins to trail a wet path of kisses down his shoulder, to his collarbone, and then his sternum. Dean doesn't object, either, when he uses the hand that's not balancing him above Dean to squeeze one of his nipples, rolling it between his index thumb and finger before replacing his hand with his mouth and sucking again.

"Do you believe me now?" Cas mumbles into his skin, his hot and burning and sweaty skin. "And don't lie."

"I—I could use some more convincing—" Dean gasps. Cas hums thoughtfully, the sound buzzing his sensitive nipple and making his hips twitch up—and his half-hard cock unintentionally brushing Cas's thigh.

"Can I touch you?"

" _Yes_ ," Dean practically whines, blushing immediately at how completely wrecked his voice is. Despite his eagerness, Cas doesn't expedite his fall down Dean's abdomen. He takes his time, sucking light bruises along the path of his smooth stomach. It's slow, achingly slow, but it's exactly what he needs.

So when Cas finally grips him firm at the base, all the blood drains from his body and goes straight to his dick. His hips jerk, and Cas pulls him up over Dean so his knees are pinning Dean's thighs into the mattress, so he can't move. The digging is bruising, but the sensation pales in comparison to Cas's fingers massaging Dean at the base, thumbs rubbing circles in his thighs.

"You look so hot like this, under me, needy," Cas intones, sparing no volume or intensity as he finally drags one hand up the length of Dean's cock. "I don't know how you could ever be ashamed of this—" He swirls his thumb around the tip, and Dean slams his arms down at his sides, grasping for anything to squeeze—the sheets, the comforter, a pillow  _anything_ that he can tear his desperate fingers into in order to keep from losing himself now. He does  _not_ want to come prematurely, not when it seems he's only begun this slow, delicious torture.

And Cas notices how Dean's skin puckers for his touch. Dean sees a hint of a smile as Cas uses his thumb to part the slit of Dean's cock, spreading precome all around the tip. "I had no expectations, Dean. None." He pauses, expression turning thoughtful. "No. I lied. I had one expectation: that you'd be beneath me, writhing, and begging to come."

Dean moans and rolls his head back. "Cas—Cas, please," he whimpers.

"Please what?"

Dean doesn't know what he wants until he looks down his stomach, seeing that Castiel has lowered his body, his head, just above the curve of his cock. He blows a single hot breath over the tip, and Dean shudders and closes his eyes. "Suck me, Cas."

"Suck your long, beautiful cock?" Cas asks, teasingly blowing small puffs of air over the head. "You don't understand how many nights, after just hearing your voice on the phone, I've had to take care of myself...thinking about what you taste like." His hooded eyes flares with excitement as he meets Dean's. "I finally get to find out."

Cas slides off Dean's legs and instead parts Dean's thighs. The weight being removed from Dean's lower half offered his hips the freedom to thrust up, just as Cas experimentally closes his lips over the head.

The air around him seems to go ice cold, because every ounce of heat touching his body pulses where Cas's mouth meets his length. Dean feels the swirl of tongue, the puff of breath as Cas exhales steady breaths through his mouth as he sinks deeper, taking Dean in inch by inch.

There is a silent moan on Dean's lips as he raises his ass from the mattress and brings his hands to Cas's head. He knows that during their heated make-out sessions, Cas enjoys a good hair tug, so Dean experiments with this knowledge by curling his fingers into the dark strands around his ears, pulling tight. He did  _not_ expect to elicit the most freaking dirty moan  _ever._ And he completely underestimated how much the low, steady vibration stimulated him. 

Cas is bobbing, licking, sucking, doing things to Dean and making him whimper and whine for more. Cas pulls his lips off, grazing his teeth along the shaft as he goes, and then presses a firm, tongue-filled kiss to the tip. "Perfect," he promises, running the index finger along the throbbing vein, down to the base and to Dean's testicles. Dean flinches, the skin so sensitive that he's sure he'll come if Cas touches him again.

"Fuck me," Dean says, and the words shock him as much as they do Cas. Embarrassment coils in his stomach, blush filling the pale skin under his freckled cheeks to match.

"Really?" Cas whispers, soothing Dean's embarrassment by pressing a hand to the curve of his thigh. There is a flare of uncertainty behind his questioning blue eyes, which Dean matches as well. Minutes ago, he was ashamed, embarrassed that he couldn't fill Cas up as well as he thought he could, fuck him senseless like he'd imagined. He hadn't even considered that maybe he'd bottom out. Previously, the dynamics of their relationship kind of indicated that Dean was the bossy, strong one. The stereotypical top. But now it was painfully—and  _not_ so painfully—clear that he enjoyed being held down with firm, adoring hands and now he can't get the picture of Cas pounding him into the mattress out of his head.

And  _fuck,_ if Cas couldn't fuck him thoroughly, no one could. He doesn't want anything else anymore. He's sure.

"Yeah," Dean breathes. "I...I want you to hold me down and work me open, and then I want you to fuck me...I want to feel all of your cock in me..." He's babbling, countless images filling his mind and making his blood pulse red and hot with new abandon.

Cas moves away, his hands, his touch, leaving Dean as well and leaving him feeling cold. He doesn't have time to register any thoughts of rejection before he realizes that Cas is just reaching into his nightstand, to pull out a bottle of lube. He squirts some into his fingers and settles back between Dean's legs.

"I want you to lay still, Dean," Cas says, working his hands beneath Dean's ass. He lifts his hips in response, granting him easier access to—to  _it._ The little hole that he'd never let any fingers venture inside unless they were Cas's. The new fantasies running over in his mind are reserved for Cas and only Cas, and with them the hole blossoms at his touch. "As much as I love to see you squirm, I want you to not pull or push. Just let me make you feel good."

He massages Dean open with careful tenderness that burns Dean in more ways than one. One finger presses inside, kneading the muscle as Cas's lips press kisses to the inside of his thighs. Then he adds another finger, scissors it, spreading Dean open just a little wider. The pain is manageable, fading the deeper Cas goes—

Dean's hips writhe as all pain and discomfort is obliterated, replaced with pleasure and pure  _electricity_ that pulses through each muscle and artery and thought until it reaches his throat and causes a moan. Cas brushes the bundle of nerves again and Dean's reaction is equally astounding.

"H-holy jesus fuck, Cas, don't stop, please," he cries hoarsely.

Cas responds by adding a third finger, less than careful now that he's found Dean's prostate. As he continues to stroke and fill Dean up from the inside, he refrains too much touching, because Dean is  _so close_ he can taste that hard, sweet flavor that fills his mouth when he comes.

"Are you ready for me?"

" _Yes_ ," Dean nearly screams, bucking his hips a little when Cas removes his fingers. He then hears the ripping of foil and frantically sits up to see Cas running a hand up his own cock— _sweet mother of fuck_ it looks even bigger all swollen and needy and Cas looks completely wrecked—as he prepares to push a condom down over it. "Cas, no condom, I want it to be just us." There are each other's firsts, after all, and it's part of his little fantasy—feeling the hot burst inside him when Cas comes.

Cas makes a sound that sounds frustrated, a growl, as he grabs Dean's thighs and pushes his knees toward his stomach. The tip of his length presses against Dean's entrance. "Relax, Dean," he whispers, pressing in a little deeper as Dean exhales a calming breath. He opens wider, wide enough for the tip to breach the ring of muscles. He's so  _thick,_ but the burn is steady and he knows it'll be gone as soon as—

 _Fuck—_ Cas isn't even all the way in when the tip brushes his prostate and he clenches. He forces his orgasm to stay at bay, digging his blunt fingernails into his palms. Cas pushes in further, until there is no inch left unfilled, no piece of flesh that isn't ruined and spoiled only for Cas. Dean is more positive than ever that there is no  _after Cas—_ there is them and there is them forever, bound and entangled into one being.

Seamless.

"I'm—close," Cas moans between thrusts, and it occurs to Dean that's gonna come without any attention his cock, which makes his skin burn a little hotter. He reaches up, dazed and grazes his fingertips from Cas's sternum do the center of his chest, resting on his heart. There is looking, and then there is seeing. Dean can see infinite wonders in his blown pupils, so much love, so much  _adoration—_ and he can't help but reflect it back with a strained smile.

"Come in me, Cas," he asks hoarsely. And he does, pulsing hot liquid inside Dean. Dean gives his body permission to let go and Cas hits his prostate again and again until he's coming in white streaks across his belly, a little spurting onto Cas's chest, too. They ride the waves of both of their climaxes until Cas finally collapses onto Dean, limp cock still buried in him to the hilt.

After a few minutes, Cas does finally pull out and simply lay across Dean, mouth whispering lazy kisses into his neck as Dean strokes his hand down his back.

"That...that was awesome," Dean says breathlessly. "I can't believe I—we—"

"Me neither," Cas agrees, leaning back so their eyes can meet again. "I never thought you'd let me do that."

"I guess that things aren't how we imagined. Heh." Dean swallows. "I definitely wanna do that again."

"Me too. But Dean," Cas says and presses a chaste kiss to the side of his mouth. "Just because there is a size difference doesn't mean I don't want you to...to fuck me, someday. Soon."

Dean's eyes widen. "But—I...really?"

Cas laughs. "Stop asking me really, as if you're shocked. Of course I do. And now that you know how good it feels... it doesn't matter how long you are because I  _know_ you're gonna fill me up and it's going to be perfect." He pauses, smiling a little, which makes Dean's chest go fuzzy. "No freaks outs. Do you understand?"

"Yeah," Dean agrees with a lazy smile. "I think I get it now."


End file.
